Digital Signatures Without Random Oracles

In Eurocrypt 2007, Camenisch, Hohenberger and Pedersen introduced the notion of multi-signer batch verification and proposed several efficient and practical batch verification schemes for signatures, including a very efficient batch verification scheme for a multi-signer setting without random oracles. This scheme is the most efficient in comparison with other existing schemes, but it can be applied only to the multi-signer setting. We observe that amongst all existing batch verification schemes, the fastest scheme for a single-signer setting is based on the BLS short signature whose proof need resort to random oracles. It is clear that batch verification for a single-signer setting is as important as for multi-signer scenarios in some applications, especially where the system has only a single signer, such as a secure time-stamping server or a certificate generation server. However, to our knowledge, the efficient batch verification of short signatures in a single-signer setting without random oracles is a challenging open problem. In this paper, we propose a new signature scheme from Gentry IBE that is as efficient as the BLS short signature scheme in batch verification. We are able to prove its security without random oracles. Our signature is approximately 320 bits in length, and a verification requires only two pairings for verifying n signatures from a single signer.

Kakvi and Kiltz (EUROCRYPT'12) proposed the first tight security reduction for RSA full domain hash signature scheme (RSA-FDH) with public exponent e < N1/4 in the random oracle (RO) model, and they left an open problem which called for a tightly secure RSA-FDH for N1/4 < e < N. In this paper, we consider the improved RSA (iRSA) trapdoor functions, introduced by Cao (Science in China'01), are functions that the security can be strictly proved to be equivalent to the factoring. We show that iRSA-FDH has a tight security reduction for e < N. Technically we construct iRSA lossy trapdoor functions, and then we apply the lossiness of the iRSA trapdoor functions to obtain tight security reductions for iRSA-FDH in the RO model. Finally, we propose a tightly secure blind signature scheme based on our iRSA lossy trapdoor functions in the RO model.

Certificate-based verifiably encrypted signatures from pairings

Electronic voting is an alternative mechanism of ballot based voting which empowers voters to cast their secret and secure vote electronically over a public channel. Many onward-thinking countries are adopting the electronic voting system to upgrade their election process. E-voting system is more complicated to construct. Thus it expects more security as compared to the postal voting system. The objective of the paper is twofold. Firstly, we proposed an efficient blind signature scheme using the identity-based cryptosystem in the random oracle model. The proposed scheme uses the combination of Boldyreva’s blind signature scheme and Choon-Cheon’s Identity-based signature. Additionally, we reduce its security to the Gap Diffie-Hellman Complexity (GDH). Under the adaptive chosen message and ID attacks it is secure against existential forgery attack. We show our proposed system performed better as compared to existing systems. Secondly, we construct an E-voting system based on our ID-based blind signature and Boneh’s short signature scheme (EVS-ID-BS) that fulfills the E-voting security requirements. To the best of our knowledge, EVS-ID-BS is the first practical implementation of E-voting system based on ID-BS Scheme which is constructed in the random oracle model. Proposed EVS-ID-BS scheme provides batch verifiability for a significantly large number of voters, needs less bandwidth cost and require less interaction with election authority.

Attribute-based signatures allow a signer with a set of attributes to anonymously sign a message about some signature policy. However, in the environments that require accountability and preventing abuse, the anonymity revocation function is vital important and necessary. In order to meet the requirements that multiple different authorized participants can sequentially aggregate and sign the same message while maintain the accountability of the signers, we propose a secure and traceable attribute-based sequential aggregate signature scheme with multiple attribute authorities. It is based on the flexible threshold access structure, and it also supports extension to any linear secret sharing scheme access structures. Our scheme can be proved secure under the CDH assumption and subgroup decision assumption in the selective model without random oracle. The security analysis shows that our attribute-based sequential aggregate signatures scheme can realize existential unforgeability, traceablity and unlinkability. It is believed that it can also be widely used in e-commerce and e-government related applications.KeywordsAttribute-based signatureSequential aggregate signatureMultiple attribute authoritiesTraceabilityUnlinkability

We propose a leakage-resilient Identity-Based Encryption IBE scheme in the relative leakage mode. The semantic security of the proposed scheme is proved in two ways in the random oracle model under the Decisional Square Bilinear Diffie-Hellman D-Square-BDH assumption. Compared with some existing leakage-resilient IBE schemes, our construction enjoys a shorter parameter length, a lower computation cost and a higher ratio of the key leakage for the same level of security.

Password-based Authenticated Key Agreement (PAKA) protocols are widely used in wireless mobile networks, however many existing PAKA protocols have security flaws. In the 3GPP2 network, there are several PAKA protocols proposed to enhance the security of the Authentication Key distribution mechanism which is subjected to the Man-In-The-Middle attack. We point out the security flaws of such protocols in [10,6] and give two practical attacks on them. Moreover we propose an enhanced PAKA protocol which can resist both undetectable on-line and off-line password guessing attacks, and formally analyze its security in the random oracle model. In addition, we consider a special version of Diffie-Hellman problem called Degenerate Diffie-Hellman problem and propose two assumptions called Computational and Decisional Degenerate Diffie-Hellman assumption which are as difficult as CDH assumption and DDH assumption respectively.

Recently, the notion of the key-insulated public- key system has been suggested to protect the security of users' private keys. A general idea of this system is changing the user's private key along with the time, but the user's public key remains unchanged. In this paper, we propose a new identity (ID)-based key-insulated signature scheme from bilinear pairings. As compared with the recently proposed ID-based key-insulated signature schemes, our proposed scheme has better performance in the batch verifying phase. For security analysis, our scheme is a provably secure key-insulated signature scheme in the random oracle model and under the computational Diffie-Hellman assumption. Meanwhile, to demonstrate the additional advantage of a key-insulated signature, we present a novel application based on the proposed scheme, called full delegation ID-based proxy signature scheme with time restriction. To our best knowledge, no such a proxy signature scheme is proposed until now.

A unified framework of identity-based sequential aggregate signatures from 2-level HIBE schemes

A newly developed signature scheme, namely the Easy Simple Factoring-based (ESF) signature scheme is proposed in this paper. First, we construct a standard identification scheme based on the ESF assumption. Then, the standard identification scheme is converted to a signature scheme by utilizing the Fiat-Shamir transformation. Our signature scheme is provable secure in the random oracle model, and the security proof is shown. The efficiency analysis of our scheme is conducted and compared with the Full Domain Hash (FDH) signature scheme. Our scheme has a more powerful efficiency performance in signing and verifying algorithms than the FDH signature scheme when the public keys u and γ in our signature scheme are fixed to small bit lengths.

Simulation-sound trap-door commitment (SSTC) schemes are an essential ingredient for making non-malleable and universally composable protocols. In previous work, the SSTC schemes and their variants are all constructed in the same framework based on digital signatures. In this paper, we provide new constructions of SSTC schemes using encryption, which is somewhat surprising, because of the tight relationship between SSTC and digital signature schemes. Although our constructions require a few rounds of interactions between a committer and a receiver and the notion of public-key encryption could be stronger than digital signature, the resulting instantiations are much more efficient than these based on digital signature schemes. In particular, we present an efficient SSTC scheme under the CDH assumption in the bilinear groups, with a tight security reduction and short public key parameters, and the first efficient SSTC scheme under the factoring assumption. Our interactive SSTC schemes inherit properties of the non-interactive version of SSTC schemes to construct non-malleable and universally composable protocols.KeywordsSignature SchemeCommitment SchemeDigital Signature SchemeChallenge CiphertextDecryption OracleThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

An efficient and provable certificate-based proxy signature scheme for IIoT environment

As a variation of ordinary digital signature scheme, a proxy signature scheme enables a proxy signer to sign messages on behalf of the original signer. Proxy multi-signature is an extension of the basic proxy signature primitive, and permits two or more entities to delegate their signing capabilities to some other entity. Many identity-based proxy multi signature (IBPMS) schemes using bilinear pairings have been proposed. But the relative computation cost of the pairing is approximately more than ten times of the scalar multiplication over elliptic curve group. In order to save the running time and the size of the signature, in this paper, we propose an IBPMS scheme without bilinear pairings. We also prove the security of our scheme against adaptive chosen message attack under random oracle model. With the running time being saved greatly, our scheme is more applicable than the previous related schemes for practical applications.KeywordsDigital signatureIdentity-based cryptographyProxy-multi signatureElliptic curve discrete log problem

In this paper, we present three digital signature schemes with tight security reductions in the random oracle model. Our first signature scheme is a particularly efficient version of the short exponent discrete log-based scheme of Girault et al. (J Cryptol 19(4):463---487, 2006). Our scheme has a tight reduction to the decisional short discrete logarithm problem, while still maintaining the non-tight reduction to the computational version of the problem upon which the original scheme of Girault et al. is based. The second signature scheme we construct is a modification of the scheme of Lyubashevsky (Advances in Cryptology--ASIACRYPT 2009, vol 5912 of Lecture Notes in Computer Science, pp 598---616, Tokyo, Japan, December 6---10, 2009. Springer, Berlin, 2009) that is based on the worst-case hardness of the shortest vector problem in ideal lattices. And the third scheme is a very simple signature scheme that is based directly on the hardness of the subset sum problem. We also present a general transformation that converts what we term $$lossy $$lossy identification schemes into signature schemes with tight security reductions. We believe that this greatly simplifies the task of constructing and proving the security of such signature schemes.

Based on the newly introduced d-decisional Diffie-Hellman (d-DDH) intractable problem, a signature scheme and a multi-signature scheme are proposed. The main method in the constructions is a transformation of a knowledge proof on the equality of two discrete logarithms. The two schemes are proved secure in the random oracle model and the security reductions to the d-DDH problem are tight. Moreover, one can select different d for different security demand of applications. Thus the schemes are secure, efficient and practical.